During the current funding period, we have developed a method for enhancing ethanol self-administration in mice. When C57BL/6J mice are offered access to ethanol for a short period during their circadian dark period, they will ingest significant quantities, reaching blood ethanol concentrations greater than 100 mg% (Rhodes et a/.,2005). The animals show signs of behavioral intoxication (Rhodes et al., in press). The current proposal is built around the production of replicated lines of mice selected for their propensity to high drinking in the dark (HDID). The experiments will further develop and characterize the model and provide selected lines for other INIA projects. HDID1 mice will be selected from HS/Npt control stock for their high (>150 mg-%) blood alcohol levels on the second day of 2 daily exposures to 20% ethanol for 2-4 hr/day, starting in hr 3 of their circadian dark cycle. A second replicate of this line (HDID2) will be started in the first renewal year, using the same selection index. If studies in the mean time (Aim 2) indicate that some modification of the test (e.g., multiple bottles) has resulted in a better selection phenotype, the HDID2 line will be started using the improved phenotype. A third replicate (HDID3) will be started in Renewal Year 3. Five phenotypes will be systematically evaluated in the selected lines vs the 8-way cross control lines as potential correlated responses to selection: Two-bottle EtOH preference, Scheduled access to ethanol (SHAG procedure), Prolonged access, The Alcohol Deprivation Effect, and Withdrawal induced Drinking after inhalation exposure. We will adapt the DID test to very young mice and study its developmental onset and time course. We will employ a chronic intermittent stress paradigm post-weaning, pre-pubertal mice of the HDID lines and controls and assess the DID phenotype in adulthood. Col Dr. Tamara Phillips will examine the effects of several test compounds on DID, using intracranial injection sites based on INIA targeted circuits. We will initially target the lateral septum and its afferent and efferent connections. Finally, we will breed additional naive mice and ship them to other interested investigators.